1. Field of the Invention
The present invention relates to a method for calcining a cathode ray tube and, more particularly, to a method for calcining a film, that can shield electromagnetic wave or prevent static electricity, on a face panel for a cathode ray tube.
2. Description of Related Art
Generally, a face panel of a cathode ray tube manufactured through an assembly line goes through a coating process of a nonglare film, an antistatic film, an antireflection film, or/and an electromagnetic wave-shielding film.
U.S. Pat. No. 5,660,876 to Kojima et al. discloses a method of manufacturing a cathode ray tube with a nonglare multi-layered film comprising at least a visible light absorbing layer containing a black dye, and an antistatic layer containing an inorganic metal compound used as a conductive agent.
U.S. Pat. No. 5,523,649 to Tong et al. discloses a video display panel having a multi-layered antireflective coating.
U.S. Pat. No. 5,652,477 discloses a display device having a multi-layered antistatic/antireflective coating.
The electromagnetic wave-shielding film for interrupting the electron waves is usually made of a single-layered structure having a silica layer or a dual-layered structure having antistatic and silica layers.
The antistatic layer comprises a transparent conductive coating layer made of a material selected from the group consisting of an ITO and ATO or comprises a thin metal layer made of Ag, Ag/Pd. The silica layer is made through a sol-gel method. As a well-known method for forming a silica film, water is added to silicon alkoxide for an hydrolysis reaction. Alcohol is used as a common solvent of the silicon alkoxide and the water. In addition, acid is used as a catalyst to derive hydrolysis and polycondensation so as to form a thin film.
Describing more in detail, in the sol-gel method for forming a silica thin film, the silica film is made through a silica sol composition, coating, drying, and heating treatment processes. That is, composition of the silica sol is realized by adding a predetermined amount of water to a precursor such as, for example, a tetraethyl-o-silicate or a tetramethyl-o-silicate so as to derive hydrolysis reaction. At this point, since the silicon alkoxide is hydrophobic, a common solvent such as ethanol, methanol, or butanol is added. After this, catalyst is further added to provide a sol particle structure that is suitable for being formed into thin film by a spin coating process or a dip-coating process and for accelerating hydrolysis reaction and polycondensation reaction.
Generally, when the silica layer is coated on the face panel, it is calcined at a temperature of about 300.degree. C. using, for example, a ceramic heater so that the organization of the film is fined and the attachment thereof can be stabilized. This calcination process is performed as a final process for making the cathode ray tube so as to prevent the surface of the silica film from being physically and chemically damaged.
However, since the calcination process is locally performed in the face panel of the cathode ray tube, resulting in thermal expansion difference between the panel, explosion proof band, and a funnel, there is a drawback in that the cathode ray tube can be cracked. In addition, since the phosphor layer can be damaged by the high temperature, the quality of the cathode ray tube is deteriorated. Furthermore, gas is generated inside the cathode ray tube by thermal decomposition, deteriorating a degree of vacuum.